richardson



No. muss. Patented Sept. 20, I898. c. H. mcmuznsou & L. McMAKIN, In. RHEOSTAT.

(Application filed Feb. 3, 1898.) (No Iodel.) 3 Sheets-Sheet 3.

WITNESSES: INVENTORS UNITED STATES PATENT OFFICE.

CHARLES H. RICHARDSON AND LEVIS MCMAKIN, JR., OF PHILADELPHIA,

PENNSYLVANIA, ASSIGNORS TO THE S. S. TUBING COMPANY, OF SAME PLACE.

IVHITE DENTAL MANUFAC- RH EO STAT.

SPECIFICATION forming part of Letters Patent No. 611,185, dated September 20, 1898.

Application filed February 3, 1898. Serial No. 669,033. (No model.)

To all whom it may concern.-

Beit known that we, CHARLES H. RICHARD- SON and LEWIS MGMAKIN, J r. citizens of the United States, residing at Philadelphia, in the county of Philadelphia and State of Pennsylvania, have invented certain new and useful Improvements in Rheostats; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

Our invention relates to certain improvements applicable to rheostats of the class employed in connection with dental cataphoresis, in which an electric current of very low amperage is used.

Our improvements relate particularly. to that type of this class of rheostats of the shunt principle, although some of our improvements are applicable to rhcostats of the series principle.

The object of our invention is to improve the construction, operation, and efficiencyof rheostai's of the class above named; and to this end our invention consists, first, of a rheostat of novel construction and means for operating the same, and, second, of improved electrical connections whereby the current in the working circuit may be reduced to zero, as will be more fully described hereinafter and then pointed out in the claims at the end of the specification.

In the accompanying drawings, which show the preferred manner of carrying our invention into effect, Figurel is atop or plan view of our improved rheostat. Fig. 2 is a vertical central sectional view of the same. Fig. is an inverted plan view of the rheostat with the bottom or base removed. Fig. at is a perspective view of the under side of the rheostat-plate, showing said plate in an inverted position, detached. Fig. 5 is a diagram illustrating the electric circuits and connections. Fig. 6 is an end view of the spring of the contact-arm, showing the point of contact with the main resistance.

\Ve will first describe the improved rheostat and means for operating the same and next the electrical connections whereby the current in the Working circuit may be reduced to zero.

The rheostat consists of rheostat-plate A, preferably circular in form and which may be of slate or other suitable non-conducting material. This plate is provided on its under side with a track or surface A for the resistance medium or material, which we prefer should be of graphite. we prefer that the portion of the rheostat-plate which constitutes the track should be of increased thickness as compared to the remainder of the plate and that it should be circular in form, except that it is broken or interrupted at one point in order to provide ends or terminals A A with a space between them.- The graphite, which is indicated at a, is smoothly and thinly spread upon the surface of the track and constitutes the main resistance of the rheostat, as is well known. A suitable contact arm or lever B, pivotally mounted in the rheostat-plate and provided with a springcontact 13, is adapted to be moved over the face of the resistance track or surface in order to throw more or less of the resistance into the circuit for regulating the current. The particular means herein shown for controlling the movements of the contact-arm and which we claim as a part of our invention will farther on be described.

The rheostat-plate A is supported upon and constitutes the top or cover of a box or case, shown as consisting of a circular base-piece O and a cylindrical side portion D, the box or case thus formed being preferably constructed of wood. The rheostat-plate A and the base-piece G are each connected to the cylindrical side portion D by means of screws a and b, respectively. The contact-arm is connected to and moves with a hub E, mounted to turn in the center of the rheostat-plate, the manner of mounting the hub being shown as follows: The rheostat-plate is provided with a central opening in which a metallic bearing or bushing F is secured, this bushing being provided with a top flange f, adapted to rest upon the top of the rheostat-plate, and is securely held in place by means of a nut f, screwing upon the lower exteriorly-threaded marked in any other desired manner.

portion of the bushing and screwed up tight against the under side of the rheostat-plate. The hub E is fitted to turn in the bushing, and a circular flange e on the lower end of the hub bears against the bottom of the bushing or against the nut f thereof. A washer e is fitted on the hub and rests against the top of the bushing, and a lug e on the hub E, engaging a notch in the washer, serves to cause the washer to move with the hub. A nut G, screwing upon the upper exteriorly-threaded portion of the hub which projects above the rheostat-plate, is screwed down upon the washer e and prevents the hub from endwise movement in the bearing or bushing, while leaving it free to be turned therein. An operating handle or knob H is fitted upon the upper portion of the hub, which above the nut G is reduced in diameter and exteriorly threaded. A lug g on the side of the hub enters a notch in the side of the opening of the handle or knob and causes the said knob and hub to turn together, while a nut I, screwing upon the hub, serves to lock the knob and hub together. Obviously the turning of the knob or handle in opposite directions correspondingly moves the contact arm or brush over the surface of the main resistance. Rigidly projecting from the base-piece O is a post J, having detachable connection with said base-piece, as by the nuts j j, screwed upon the post on opposite sides of the base-piece. The post J passes through the hub E, which for this purpose is made tubular, and an index finger K is carried at the upper end of the post. The handle or knob H is recessed on top, and the bottom of the recess is covered by a dial-plate L, and the post J projects slightly above the dial-plate through a central opening therein, so that the indexfinger may be attached to the post by way of its hub, which passes through the opening in the dial-plate, as will be readily understood. The dial-plate is suitably marked, in this instance, from O to 100, or it may be It is covered by a crystal H, and it will be seen that when the handle or knob is turned to regulate the current by movement of the contact arm or brush the dial-plate is turned, while the index finger remains stationary relatively to the rheostat.

The apparatus so far described is applicable, it will be seen, to either a shunt or series rheostat, and the mechanical construction possesses certain advantages, among which maybe stated the following: The case is simple, strong, and durable and may be readily put together and taken apart. The rheostatplate A not only serves as the resistance-track for supporting the resistance material ormedium a, but also serves as the top or cover for the case. The said resistance medium being entirely inclosed is subjected only to the practically unappreciable wear of the contact-arms, whereas it has been found that in rheostats of -this class which employ a slate or other non-conducting plate covered with graphite as the resistance medium, if the same is exposed, it sooner or later becomes worn off and the efficiency and accuracy of the apparatus impaired or altogether destroyed, not by reason of the movement of the contact-arm over the resistance medium, but by contact of external objects, such as the contact of the fingers or a cloth used to remove dust or dirt which necessarily accummulates uponthe resistance medium and which must be removed. Owing to the comparatively large size of the handle or knob which carries the movable dial-plate the contact-arm may be moved with greater steadiness and firmness and the current controlled with greater accuracy and nicety than is possible with the ordinary form of rheostat, in which the index-finger is moved instead of the dial-plate.

We have herein shown our improvements as applied only to a rheostat of the shunt principle, and the electrical circuits and connections thereof will now be explained.

Referring particularly to the diagram shown in Fig. 5, the positive wire K from the battery is connected to the rheostat by way of a coupling-socket in the side of the casing D, and a Wire or current-lead L connects with this coupling-socket and with one end A of the main resistance at Z. A wire or current-lead M, connected at m to the opposite end A of the resistance, connects with another coupling-socket n, also in the side of the casing and adapted to receive the coupling end of the negative battery-wire N. A switch for turning on and off the current may be located in the wire M between the end A of the re sistance-track and the coupling-socket n, or, if desired, the switch may be located at any point in the main or direct circuit. This switch, which may be of any suitable wellknown form, is shown as consisting of a plate 0, secured to the side of the casing, and to which one end of the wire M is connected, a lever O, pivoted to said plate and provided with a knob or handle,which projects outside of the side casing, and a fixed contact 0, to which the other end of the wire M is connected. This completes the direct circuit of the rheostat, the shunt or working circuit being as follows: Aconductor or wire P, connected at p to the same end A of the resistance with which the wire or lead L is connected and which extends farther into said resistance than the wire L, for a purpose farther on to be explained, is secured to a coupling-socket P in the side D of the casing opposite the coupling-sockets 70 n and in which fits the coupling end of the positive wire Q of the working circuit. Another conductor or wire R is connected to a metallic strip S,which is electrically connected to the contact-arm B by way of its arm and hub E and the bushing F, and the wire R is connected at its opposite end to a coupling-socket T in the side D near the coupling-socket P and with which the negative wire W of the working circuit is adapted to be coupled.

The ends of the wires or leads L, P, and M are best attached to the ends of the resistance at Z, 1), and m, respectively, in the following way: Grooves are cut in the top of the resistance-track at and near the ends thereof at points where the wires are to be connected thereto, each of these grooves extending from the end of the track inwardly or toward the body of the track a suitable distance. The ends of the wires or leads are each placed in its proper groove in the track and secured in place by means of paste, preferably composed of the same substance (graphite) of which the resistance medium is composed. After the paste filling the grooves has hardened it is smoothed olf flush with the surface of the resistance medium, so as to present a smooth uninterrupted surface over which the contactarm may be moved.

The wires L P M, connecting the ends of the main resistance and the coupling-sockets is, P, and a, respectively, as well as the wire R, connecting the contact-arm wit-h the coupling-socket T by way of the strip S, are properly insulated, are contained inside the rheostat, and are for convenience placed in a groove d, cut on the interior surface of the side portion D of the case, whereby there is no danger of the wires becoming entangled with the movable contact-arm. The coupling-sockets, which, if desired, may be replaced by bindingposts, are located in the side D in pairs on opposite sides of the rheostat. The coupling sockets 7i; and n for the battery-wires are near each other on one side of the rheostat, while the coupling-sockets P and T for the wires of the working or patients circuit are near each other on the opposite side of the rheostat.

The operation of the improved rheostat so far described is as follows: Vith the switch 0 closed and the contact-arm B resting at or near the end A of the main resistance, which is permanently connected to the working circuit and resting against an adjustable stop formed, in this instance, by a screw U, working in a bracket or lug u, projecting from the bushing F, or rather from the nut f of said bushing, the current will enter the rheostat through the wire K, coupling 7e, and wire L. It will then pass through the resistance a and out through wire M and switch 0 to contact at and then back to the battery by wire N. 13y moving the contact-arm away from the end A of the resistance the current will be divided and a portion of it will be shunted through the wire P to couplingsocket P, wire Q, to the positive electrode V of the working circuit, through the objectto which the shunt circuit is to be applied, then by way of the negative electrode 7 of the working circuit, wire to the couplingsocket T, then through wire R to metallic strip S, and through contact-arm B. The shunt-current will then join the main current passing through the main resistance and will pass to battery with the same by way of wires M and N, as before explained. The farther the contact-arm is moved away from the end of the main resistance, before mentioned, the greater will be the resistance between said brush and the end of the track, and consequently the greater will be the amount of the current shunted through the working circuit. The amount of current passing through the working circuit can therefore be regulated by movement of the contact-arm.

In all rheostats of the shunt principle heretofore constructed for use by dentists in cataphoric operations there is always some current in the working circuit when said circuit is completed and the main circuit closed. This is true even when the contact-arm is set at the nearest approach to Zero possible owing to the resistance between the point of contact of the spring contact-arm and the end of the wire P, which connects the positive electrode V of the working circuit with the starting end A of the resistance-track at p, the resistance being caused by the graphite interposed between said point of contact and said wire. In rheostats of this character turning the current on will drive a current through the working circuit by an instantaneous jump from nothing to some considerable amount, which, in the case of dental cataphoresis, is Objectionable for the reason that the least current, no matter how small, passing through the sensitive membrane of a patient before the same has been obtunded may be exceedingly painful. A perfect rheostat for dental cataphoric purposes, therefore, should be susceptible of not only increasing the current in the working circuit by gradual amounts, but also of decreasing this current to absolute zero, so that no current would pass through the working circuit even when current is still passing through the main resistance. It will be understood that the electrical conditions necessary to produce such a result require that there should be no difference of potential between the contact-spring B of the contact-arm and the connection of the wire P with the graphite track.

In order to overcome the objection in the ordinary form of rheostats above pointed out and to produce a rheostatin which the current in the working circuit may be reduced to absolute zero and very graduallyincreased as desired by movement of the contact-arm, we have arranged the electrical connections of our rheostat as will next be described. Instead of connecting the conductor P of the shunt-circuit with the main resistance on a line with the point of connection of the current-lead L of the electric supply with said main resistance the conductor P is connected to said resistance at a point between the main current-leads L and M. This may be accomplished in the following manner: The terminal p of the wire or lead P is extended farther into the resistance-track from the end A in the direction in which the said contactarm is moved to start and increase the current shunted through the working circuit than the terminal Zof the current-supply wire L. This relative arrangement of the terminals of the wires P and L in the resistancetrack allows of the point of contact b of the contact-spring B being moved past the point 1) toward the end A of the main resistance and rest on the said resistance between the terminals 19 and Z. When in such position, the point of contact of the spring-contact B is nearer the terminal Z than the terminal p is to said terminal Z, and from causes well known to those skilled in electrical art the direction of the current in the working circuit will be reversed relatively to the direction it takes when the contact-point of the arm is moved beyond the terminals 19 and l in a direction away from the end A of the main resistance. It will be seen that this arrangement provides for placing the contactarm in two positions near together where the current in the working circuit may be caused to flow in opposite directions according to the position of the contact-arm and that consequently there In ust be a point between these two positions of the contact-arm where the current changes its direction, or, in other words, where the current has no direction and in fact where there is no current at all. When this zero-point has been definitely ascertained, the adjustable stop U is set to prevent the contact-arm from going beyond said point. In this way when the contact-arm rests against the adjustable stop, which position of the contact-arm is externally indicated by the figure O on the dial-plate, being opposite the pointer K, as shown in Fig. 1, the electrodes V and W may be applied and the switch 0 closed without there being any current whatever in the working circuit and that by moving the contact-arm very slowly away from the adjustable stop the current in said working circuit may be Very gradually and evenly started and increased from zero to the desired strength, it being understood that as the sensitive membrane of the patient becomes gradually obtunded the strength of the current may be correspondingly increased without causing pain.

It should be understood that many changes may be made without departing from our invention and that some of the improvements may be used without the others. For instance, the case or box and the controlling and indicating mechanism, the details of construction of which may be varied, may be used with resistances and electrical circuits and connections differing from those described herein, and, conversely, the means employed for enabling the current in the shuntcircuit to be started from zero and very gradually increased by movement of the contactarm may be used in connection with rheostats differing from the one herein shown and described.

We claim as our invention 1. The combination, in a rheostat, of the case consisting of a base-piece, a side portion to which said base-piece is connected, and a top or cover of non-conducting material connected to said side portion and constituting the rheostat-plate, said plate being provided on its inner or under side with a resistancetrack, a contact adapted to be moved over the surface of the resistance-tracl ,'the arm of said contact being pivotally mounted in said rheostat-plate, means outside of the case and above the rheostat-plate for moving the said contact, and means also outside of said case for indicating the position of said contact, substantially as and for the purpose herein set forth.

2. The combination, in a rheostat, of the case, the resistance-track, the movable contact-arm, the handle for turning said contactarm provided with a dial-plate, and the index supported in fixed relation to the rheostatcase, substantially as and for the purpose herein set forth.

3. The combination, in a rheostat, of the case consisting of the base, the side portion, the top plate, the resistance-track, the movable contact-arm, the tubular hub of which is mounted to turn in the top plate, the handle or knob connected with the hub of the movable contact-arm, and provided with a dial movable with said handle or knob, a post supported in fixed relation to the case and projecting through and above the tubular hub of the contact-arm, and the index supported upon the said post, substantially as and for the purpose herein set forth.

4. The combination, in a rheostat, of the main resistance, current leads or wires elec trically connecting the main resistance with the electric supply-circuit, the shunt-circuit, one conductor of which is connected to the main resistance at a point between the main current-leads, a movable contact in electrical connection with the main resistance, and means for limiting the movement of said movable contact relatively to the point of connection between the conductor of the shunt-circuit and the main resistance, whereby the current in the shunt-circuit may be started from zero and very gradually increased by movement of the movable contact, substantially as and for the purpose herein set forth.

In testimony whereof we affix our signatures in presence of two witnesses.

CHARLES H. RICHARDSON. LEWIS MOMAKIN, JR. Witnesses: G. HERBERT JENKINS, THEODORE B. VAILL. 

